Medical pouches are typically made of a highly plasticized polyvinyl chloride (PVC). More recently, it has been proposed that such pouches be constructed of a flexible film material, as described in U.S. Pat. No. 4,643,926 to Mueller, which contains one or more layers of film including a vinyl carboxylate copolymer which enhances the radio-frequency (RF) sealability of the film. U.S. Pat. No. 4,599,276 to Martini discloses the copolymer as used in making such films and the two cited patents are herein incorporated by reference. The above referenced patents represent important steps forward in the art of providing a safe versatile autoclavable medical solution packaging material which can be RF sealed into a pouch. Such pouches are resistant to cracking and embrittlement while remaining flexible and resistant to stress. They also offer these advantages without the need for PVC in the film.
However, it has been found that vinyl carboxylate copolymer resin, such as ethylene vinyl acetate copolymer (EVA), used to enhance the RF sealability of the film, can produce acid extractables such as acetic acid following a typical autoclave sterilization procedure. These acid groups may migrate into the aqueous contents of the medical pouches, causing an undesirable pH shift of the contents. In some cases, this can result in shortening the life of the pouch contents as well as precluding certain solutions from use in such pouches.
In accordance with the invention, we have found that vinyl carboxylate copolymers such as EVA can be used to advantage in films, especially flexible films for medical applications, while at the same time reducing the pH shift problem described above. This is accomplished by including in the film structure an alkali metal ionomer.